This invention relates to a system for, and method of, providing a header for indicating to an observing station an individual one of a plurality of originating devices, and an individual one of the ports in such originating device, providing packets of data. The invention also relates to a system for, and a method of, providing a trailer for indicating whether a collision has occurred between the transmission of packets from such individual one of the ports in such individual one of the originating devices and packets from another one of the originating devices.
Systems are provided for transmitting data in packets. Each packet may have at least a particular length (e.g. at least 512 nibbles) where each nibble consists of a plurality (e.g. four (4)) binary bits. Each packet may include a preamble, a start-of-frame delimiter and data. The preamble in each packet is provided to synchronize the subsequent nibbles in the packet with clock signals. The preamble may consist of a plurality of nibbles each having the same particular format. The start-of-frame delimiter includes a plurality of nibbles indicating that data follows such delimiter. In addition to providing information, the data may include an identification of the source of the packet and the recipient of the packet.
It is sometimes desired to make a record of the individual one of the originating devices, and the individual one of the ports in such originating device, providing the packets. Two (2) different approaches have been provided in the prior art to record such information. One approach has been to provide additional signal lines to record the individual one of the originating devices, and the individual one of the ports in such originating device, providing the packets. The use of such additional signal lines is not satisfactory because it unduly complicates the construction of the system. A second approach has been to provide a trailer at the end of the packet to indicate the individual one of the originating devices and the individual one of the ports in such originating device. This is not desirable because it shortens the space between successive packets.
Sometimes two (2) originating devices transmit packets at the same time. This causes a collision to occur between the two (2) packets. Any other originating device simultaneously receiving the two (2) packets will become confused and accordingly generate wrong information. It is desirable to record the occurrence of such a collision. It is also desirable to record other information upon the occurrence of a collision. This would include the spacing between successive packets and indications of a normal packet or variations from a normal packet. No one until now has used the same lines normally used for passing the packet in order to record the occurrence of collisions, the spacing between packets and indications for each packet that the packet is normal or varies in specified ways from a normal packet.
This invention provides a system for, and method of, providing and recording the different information specified *above. For example, the system and method of this invention provide such information in a relatively straightforward manner without complicating the construction of the system. The system and method of this invention illustratively provide for a recording of the individual one of the originating devices in a plurality, and the individual one of the ports in such originating device, providing packets of information. The system and method of this invention also provide for the determination of collisions between packets simultaneously transmitted from two (2) of the originating devices in the plurality and for the indication of the occurrence of such collisions.
In one embodiment of the invention, each packet normally consists of a preamble, a start-of-frame delimiter and data. The preamble has nibbles each having a particular format. A header substituted for preamble nibbles by an individual one of the originating devices in a plurality, and an individual one of the ports in such originating device, indicates such device and such port in such originating device. Such port in such originating device sends such modified packet to others of the originating devices and to an observing station.
The header format is such that the last nibble in the header and the remaining preamble portion will not be confused with any two (2) nibbles in the header. A particular one of the originating devices indicated in the data converts the header back to the preamble format and transmits the converted packet to a receiving station. The observing station records the originating device, and the port in such device, indicated in the header.
Each packet includes at its end a trailer formed from a plurality of nibbles and indicating whether or not a collision has occurred between such packet and a packet from another one of the originating devices. The trailer in each packet may also indicate additional informationxe2x80x94e.g. whether the packet (a) is a normal packet, (b) is a runt packet, (c) is from an unacceptable source and (d) the delay between each packet end and the next packet start. The information in the trailer for each packet passes to the observing station.